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The Student Resource Disk for Java

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ã Borlandđ JBuilder 7 Personal
ã Sun Java 2 SDK Standard Edition
• Sun Java™ 2 SDK Standard Edition Documentation
• Program Files

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JONES AND BARTLETT COMPUTER SCIENCE



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Copyright © 2003 by Jones and Bartlett Publishers, Inc.
Cover image © Peter J. Robinson/Photolibrary/PictureQuest
Text photo credits follow the index, which constitutes a continuation of the copyright page.
Unless otherwise acknowledged, all photographs are the property of Jones and Bartlett
Publishers.
Library of Congress Cataloging-in-Publication Data
Dale, Nell B.
Programming and problem solving with Java / Nell Dale, Chip Weems, Mark Headington.
p. cm.
Includes index.
ISBN 0-7637-0490-3
1. Java (Computer program language) I. Weems, Chip. II. Headington, Mark R. III.
Title.
QA76.73.J38D346 2003
005.13’3--dc21
2002043476
All rights reserved. No part of the material protected by this copyright notice may be reproduced or utilized in any form, electronic or mechanical, including photocopying, recording, or
any information storage or retrieval system, without written permission from the copyright
owner.
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This book is dedicated to you, and to all of our other students for
whom it was begun and without whom it would never have

been completed.

To quote Mephistopheles, one of the chief devils, and tempter of
Faust,
…My friend, I shall be pedagogic,
And say you ought to start with Logic…
…Days will be spent to let you know
That what you once did at one blow,
Like eating and drinking so easy and free,
Can only be done with One, Two, Three.
Yet the web of thought has no such creases
And is more like a weaver’s masterpieces;
One step, a thousand threads arise,
Hither and thither shoots each shuttle,
The threads flow on, unseen and subtle,
Each blow effects a thousand ties.
The philosopher comes with analysis
And proves it had to be like this;
The first was so, the second so,
And hence the third and fourth was so,
And were not the first and second here,
Then the third and fourth could never appear.
That is what all the students believe,
But they have never learned to weave.
J. W. von Goethe, Faust, Walter Kaufman trans., New York, Anchor/Doubleday: 1963.

As you study this book, do not let the logic of algorithms
bind your imagination, but rather make it your tool for weaving
masterpieces of thought.

418

CASE STUDY
static JButton subtract;
static JButton clear;

// Subtract button
// Clear button

// Define event listener for numeric buttons
static class NumericHandler implements ActionListener
{
public void actionPerformed(ActionEvent event)
// Handle events from the buttons in calcPane
{
double secondOperand;
// Holds input value
String whichButton;
// Holds the button's name
// Get the operand
secondOperand =
Double.parseDouble(inputField.getText());
whichButton = event.getActionCommand(); // Get the button's name
if (whichButton.equals("+"))
result = result + secondOperand;
else
result = result – secondOperand;

// When the name is "add"
// add the operand
// Otherwise
// subtract the operand

register.setText("" + result);
inputField.setText("");

// Display result
// Clear input

}
}
static class ClearHandler implements ActionListener
{
public void actionPerformed(ActionEvent event)
// Handle events from the Clear button in calcPane
{
// Set result back to zero
result = 0.0;
register.setText("0.0");
// Reset result in register
inputField.setText("");
// Clear input
}
}
public static void main(String[] args)
{
operation = new NumericHandler();
clearOperation = new ClearHandler();

result = 0.0;

// Instantiate a NumericHandler
// Instantiate a ClearHandler
// Initialize result

// Instantiate labels and initialize input field
resultLabel = new JLabel("Result:");
register = new JLabel("0.0", JLabel.RIGHT);
entryLabel = new JLabel("Enter #:");
inputField = new JTextField("", 10);


CASE STUDY
// Instantiate button objects
add = new JButton("+");
subtract = new JButton("-");
clear = new JButton("Clear");
// Register the button listeners
add.addActionListener(operation);
subtract.addActionListener(operation);
clear.addActionListener(clearOperation);
// Add interface elements to calcFrame
calcFrame = new JFrame();
// Give the frame a value
calcFrame.setSize(300, 200);
// Specify size of frame
// Set close operation to exit
calcFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
calcPane = calcFrame.getContentPane();

// Get the content pane
calcPane.setLayout(new GridLayout(4,2)); // Set the layout manager
calcPane.add(resultLabel);
calcPane.add(register);
calcPane.add(entryLabel);
calcPane.add(inputField);
calcPane.add(add);
calcPane.add(subtract);
calcPane.add(clear);
// Show the frame
calcFrame.setVisible(true);
}
}
When we run the application, it displays a window like the one here:

419